This invention relates to the distribution of particles within composite plating.
Composite plating is a technology well documented and widely practiced in both electrolytic and electroless plating. Composite plating refers to the inclusion of particulate matter within a plated layer as illustrated in FIG. 1. The development and acceptance of composite plating stems from the discovery that the inclusion of particles within a plated layer can enhance various properties of the plated layer, and in many situations actually provide entirely new properties to the plated layer. Particles of various materials can provide characteristics including wear resistance, lubricity, corrosion resistance, phosphorescence, friction, altered appearance, and others.
Although composite electrolytic plating predates composite electroless plating, composite electroless plating has been developed into a well established field. A well documented survey of composite electroless plating can be found in xe2x80x9cElectroless Plating Fundamentals and Applicationsxe2x80x9d edited by G. Mallory and J. B. Hadju, Chapter 11, published by the American Electroplaters Society, 1990, incorporated herein by reference.
Early development of composite electroless plating includes the work of Odekeren in U.S. Pat. No. 3,644,183 which was directed toward increasing the corrosion resistance by the incorporation of certain particulate material. Metzger et al documented a wider variety of plated alloys and particulate materials capable of being composite plated in U.S. Pat. No. 3,753,667. In U.S. Pat. Nos. 3,562,000 and 3,723,078, Parker further demonstrated an assortment of materials including metallic particles which can be codeposited from an electroless plating bath. This early work was all directed at producing composite plated layers with a uniform dispersion of particulate matter within the metal matrix.
In U.S. Pat. No. 3,853,094, incorporated herein by reference, Christini et al disclosed an electroless plating apparatus which serves to insure the uniformity of particulate dispersion within a composite electroless plated layer. Subsequent work by Christini et al in U.S. Pat. Nos. 3,936,577 and 3,940,512, and Reissue U.S. Pat. Nos. 29,285 and 33,767 concentrated on the codeposition of diamond particles within electroless plating. These patents were similarly concerned with the uniform dispersion of particles within the plated layer.
Additional inventions in the field of composite electroless plating include the use of a wider array of particulate materials such as Yano et al in U.S. Pat. No. 4,666,786 and Henry et al in U.S. Pat. No. 4,830,889.
Feldstein taught the utility of an overlayer above the composite plated layer for smoothness advantages in U.S. Pat. Nos. 4,358,922 and 4,358,923, incorporated herein by reference.
Spencer et al illustrated the benefit of including a blend of distinct particle sizes within the composite plated layer.
Feldstein et al disclosed plating bath stability benefits resulting from the addition of particulate matter stabilizers to the plating bath in U.S. Pat. Nos. 4,997,686, 5,145,517, 5,300,330, and 5,863,616 incorporated herein by reference.
In U.S. Pat. No. 4,716,059 Kim demonstrated plating solutions with non-ionic surfactants having specific HLB numbers for composite plating graphite fluoride.
Significant work has been done in the composite plating of parts utilized in the textile industry. Herbert et al""s U.S. Pat. No. 4,193,253 relates to the composite plating of rotors with silicon carbide, incorporated herein by reference. Lancsek""s U.S. Pat. No. 4,859,494 involves open end spinning combing rolls, incorporated herein by reference.
In all of the above referenced work, the intentions and results were uniformity in particulate dispersion within the plated layer and uniformity of the composite plated layer on all surfaces of the plated articles. In U.S. Pat. No. 5,520,791, incorporated herein by reference, Murase departed from earlier work by demonstrating a non-homogenous composite plated layer for the internal surfaces of a cylinder of an internal combustion engine block wherein the density of particulate matter near the outer surface of the plated layer is greater than that of the inner portion of the coating adjacent to the substrate. In U.S. Pat. No. 5,707,725, incorporated herein by reference, Feldstein et al disclosed methods to produce composite electrolessly plated articles with a gradient in particulate density ranging from a higher density adjacent to the substrate to a lower density at the outer surface of the coating.
All of the previous work, including the Murase U.S. Pat. No. 5,520,791 and Feldstein et al U.S. Pat. No. 5,707,725, share the characteristic that the composite electroless coatings were uniform along the surface of the substrates. In U.S. Pat. Nos. 5,674,631 and 5,702,763, incorporated herein by reference, Feldstein disclosed a method of increased substrate rotation to achieve varying densities of codeposited particulate matter in the plated layer along the surface of the substrate. This invention was termed xe2x80x9cselective codepositionxe2x80x9d by the inventor. Numerous benefits for this novel method were further presented including particulate savings, cost reductions, and decreased bath loading.
The present invention is a method to provide composite electroless coatings with varying densities of codeposited particles in the plated layer along the surface of the substrate to specified area(s) of the substrate.
The present invention demonstrates a method of composite electroless plating with varying densities of codeposited particles in the plated layer along the surface of the substrate. This invention is a departure from the prior art in that it discloses a method for directing the varying densities of codeposited particle to specified area(s) of the substrate. In the prior art, the pattern of the varied density of codeposited particles in the plated layer was a function of rotational speed and geometry of the substrate. A suitable rotational speed may be found to provide a variation in density of codeposited particles in the plated layer along the surface of the substrate for articles of certain geometries. However, adjustment of rotation speed alone may not be sufficient to produce a variation in density of codeposited particles in the plated layer along the surface of the substrate for articles of other geometries in a commercially or functionally useful condition.
We have discovered that a modification of the angle of rotational axis during composite electroless plating at high rotational speeds provides the ability to direct the variations of codeposited particles in the plated layer to specific areas along the surface of the substrate. For example; articles of certain geometries are capable of being plated according to the methodology of the prior art to achieve a variation in densities of codeposited particles within the plated layer along the surface of the substrate, but this variation may not be the most desirable pattern of variation desired. Areas of the substrate where high codeposited particle densities are desired may not have the optimal particle density. Conversely, areas of the substrate where a lower particle density or no codeposition of particles is desired may receive a higher codeposition of particles than desired.
One such example can be found with the coating of a rotor cup useful in open end textile spinning. Such rotor cups may be manufactured of steel, aluminum, or boronized steel. On these cup shaped parts, there are only four areas along the substrate where codeposition of particles is necessary as illustrated in FIG. 2: the sliding wall (1), the groove (2), the groove wall (3), and the step (4), inside the cup. Codeposition of particles on the entire outer surface (5) is.unnecessary. No coating is typically applied in the bore (6) in which a shaft is installed to rotate the rotor cup for use. By fixing the angle of the rotor cup""s axis of symmetry to a value other than zero, a variation in codeposited particles within the plated layer along the surface of the substrate was achieved whereby the critical internal surfaces achieved a high level of codeposition while the outer surfaces demonstrated essentially no codeposition of particulate matter. In this one example, the present invention has made this process viable for substrates of this geometry and to realize the substantial benefits presented here and in the prior art. While this example relates to a specific article and wear resistant particles, the present invention extends to articles of any geometry and use, and composite electroless coatings consisting of any metal or alloy with particulate matter of any material. The thickness of the coating can be up to 100 microns, preferably within the range of 10 to 50 microns.
Codeposition of particulate matter within electroless plating is well documented and widely practiced. Those in the field have developed an extensive array of particles of various sizes and materials which can be codeposited within numerous metals and alloys. Wherein particles of up to 50 microns may be codeposited, with a preferred particle range typically between 0.1 to 10 microns. Since the early development of such composite coatings, the intentions of the practice were always to produce coatings with a uniformity of codeposited particles within the plated layer along the surface of the substrate. Even inventions directed at producing a plated layer with a gradient of particle densities from the inner to outer regions of the coating in relation to the substrate, were uniform along the surface of the substrate. A cross sectional view of the coating at any location along the surface of the substrate, for example, would look essentially the same as any other location along the surface of the same substrate.
The prior art which first demonstrated the ability to produce a coating with a variation in codeposited particles within the plated layer along the surface of the substrate used rotational speed to accomplish this objective for numerous benefits including particle conservation, cost reductions, and decreased plating bath loading with particulate material. This prior art, however, relied only on rotation of the substrate on a single axis which was at zero degrees to the surface of the plating bath. As in the following example, the present invention demonstrates how setting the axis of rotation to an angle other than zero degrees is able to direct the areas of differing codeposited particle densities to various areas along the surface of the substrate.